Process and apparatus for forging pistons or the like



April 3, 1956 c. A. SPARKS 2,740,519

PROCESS AND APPARATUS FOR FORGING PISTONS OR THE LIKE Filed May 26, 1952 2 Sheets-:Sheet 1 Claw/v5 Aer/we 524E165;

INVENTOR.

ATTOENEX C. A. SPARKS April 3, 1956 PROCESS AND APPARATUS FOR FORGING PISTONS OR THE LIKE 2 Sheets-Sheet 2 Filed May 26, 1952 aEoA/s Aer/we SPAR/(5,

INVENTOR. 36

BY f A-rraQ/vsy.

PR-GCESS AND APPARATUS FOR FORGIN G PISTONS OR THE LIKE.

Cleone Arthur Sparks, Pasadena, Calif., assignor to Forgedtrue Piston Corporation, Los Angeles, Calif., a corporation of California Application May 26, 1952, Serial N 290,035

7 Claims. (Cl. 207-6) This invention relates to the manufacture, by a forging process, of hollow metal objects, such as pistons for internal combustion engines.

It is now common, in the automotive industry, to employ lightweight forged aluminum pistons. Such pistons have substantial advantages over pistons made from castings of various metals, such as aluminum or cast iron. The advantages are increased strength and uniformity of grain structure, resisting failure of the pistons.

It is one of the objects. of this invention to improve, in general, the production of forged articles, such as pistons, which, after the forging operation, may be readily finished to the desired dimensions.

In an effort to produce forged pistons of this character, use has been made of an impact-extrusionprocess. In such a process, a punch cooperates with. a hollow die to operate upon a metal blank or slug in the die; and, by the speed of the punch and the pressure exerted, the metal of the blank or slug is caused to correspond to the interior configuration of the die and the exterior configuration of the punch.

When relatively simple forms of hollow articles are formed by this impact-extrusion process, it is quitefeasible to complete the forging process with one hit. However, when the internal surfaces. of the article are interrupted by substantially sized bosses and recesses. (as required, for example, to provide wrist-pin bosses), it has been necessary to form the piston by repeated hits.

It is another object of this invention to make it possible to form such piston blanks, or similar articles, with but one hit, thereby substantially reducing the cost of manufacture.

By the aid of the present invention, a single operation is sufficient, because the punch and die cooperate to ensure substantially uniform flow of metal to all, parts of the cavity formed between the punch. and the die.

It is therefore still another object of this invention to shape the cooperating surfaces of the punch and die in such manner that the flow of metal occurring during the short period of impact will fill the. cavity to the desired point, in spite of the fact that normally the resistance to the flow of metal would. be nonuniform.

The slug placed. into the die for forming the blank article often requires. preheating; for example, when an 18s aluminum alloy is used, the. slug. is preferably preheated to about 750 F. Accordingly, to reduce the. shock nited States Patent F loading when starting with. a. cold punch, it is desirable 2,740,519 Patented Apr. 3, 1956 the invention. For this purpose, there is shown a form in the drawings accompanying and forming part of the present specification. The form will now be described in detail, illustrating the general principles of the invention; but it is to be understood that this detailed description is not to be taken in a limiting sense, since the scope of this invention is best defined by the appended claims.

Referring to the drawings:

Figure l is. a diagrammatic view showing a die and punch embodying the invention, said punch being withdrawn from the die, and the view also indicating a temperature control system for the punch;

Fig. 2 is an enlarged fragmentary sectional view, taken along a plane corresponding to line 22 of Fig. 1;

Fig. 3 is a fragmentary side elevation of the operating or lower portion of the punch;

' Fig. 4 is a sectional view, showing the punch and the die in full cooperative relation at the completion of an impact-extrusion cycle;

Figs. 5-5 and 6-6 are sectional views, taken respectively along planes corresponding to lines .5---5 and 6-6 of Fig. 4; and

Fig. 7 is a sectional view of a completed blank formed by aid of the die and punch.

In the present instance, the die 1 and the punch 2 have cooperating surfaces formed to produce blanks for pistons. Such a blank is illustrated in Fig. 7. The blank 3 has a hollow skirt portion 4 and a domed head 5. Diametrically opposite wrist pin bosses 6 and 7 extend inwardly of the skirt 4. The bosses are integral with and joined to the interior surface of the domed head 5. It will be noted that the skirt is of virtually uniform length around its entire circumference and there are no outwardly or inwardly extending shoulders near or at the open end of the skirt.

This blank 3, after the impact-extrusion operation, is ready for machining. Thus, the exterior may beturned on a machine tool to a definite diameter, and piston ring grooves may be formed therein. The wrist pin bosses may be provided with appropriate bores for the accommodation of a diametrically extending, Wrist pin between these bosses 6 and 7.

The die 1 has a cavity 8 whose wall corresponds to the exteinal shape of the blank 3. As explained hereafter, cavity 8 is specially formed in order to make it possible for the blank 3 to be formed in one impact extrusion step.

The lower end of die 1 has a concave surface 39, which is partly formed by an ejector or stripper portion 38. A small vent 36 is provided. in this portion, communicating with a central well 37.

The lower end of the punch 2 is provided with a. pair of diametrically opposite recesses 11 and 12. These recesses, as shown most clearly in Figs. 3 and. 6, extend entirely to the lower convex surface of the punch 2 and provide a space into which metal can flow to form the wrist-pin bosses 6 and 7. The metal filling these recesses. 11 and 12 is illustrated in Fig. 4, corresponding to a position in which the punch 2 has moved into full cooperative relation with the die I.

These recesses extend across the leading portion 21 (Fig. 3) of the punch 2, and into a zone. 15 having a slight taper. This lead portion 21 is joined to the lower edge of zone 15 by a convex fillet 22.

The metal 13. (Figs. 4 and 6) for forming the forged article is supplied by a slug or disc 14 (Fig. 2) of appropriate material and of slightly smaller diameter than the interior surface 8 of the die 1. This lug 1'4 may be of any one of a number of appropriate aluminum alloys capable. of being forged, and its volume is equivalent to the volume of the metal forming the piston blank 3.

This slug or disc 14 may be preheated. Thus, for example, if an 18s aluminum alloy is used for the slug, this should be preheated to approximately 756 in any desired manner.

The external surfaces of the male punch cooperate with the wall of the die to form the head or dome, the wrist pin bosses and the skirt of the piston blank. The greatest portion of the skirt is formed between the wall of the die and surface 15 of the punch and the skirt wall is thin in comparison with the mass of metal in the Wrist pin bosses 6 and '1'. When the brought, at a rapid rate, into cooperative relation with the die 1, the flow of metal provided by the slug 1 3 rapidly fills the relatively large recesses I11 and 12, since the extruded metal flows in the line of least resistance during the period of extrusion. if no further provisions were made, the rise of the metal into the between the zone 15 of punch 2 and the ca would be greatly retarded, due to the restriction of the how between the closely spaced surfaces of the cavity 3 and of the zone 15 respectively. As a result, the upward flow of metal would not be uniform, certain peripheral portions being greatly in advance of other portions, and the skirt of the blank would not be of uniform length or physical characteristics, such as strength, ductility, hardness, elongation, etc. Whenever uneven flow occurs, temperature differentials occur which result in differences in grain structure and physical properties of portions of the blank (such differences being generally noticeable in areas corresponding to an'excessively retarded wave front of flowing metal), such inequalities rendering the blank defective.

This ditliculty can be overcome by providing a reduced resistance to the flow of metal at localities along the die 1 and punch 2 angularly spaced from the recesses it and 12. Thus, as shown most clearly in Fig. 5, the skirt formed in the annular space between the punch 2 and the die 1 does not have uniform thickness. At the zones or portions 16 and 17, intermediate the wrist pin boss recesses 11 and .12, the spacing of the cooperating surfaces of the die 1 and punch 2. is increased over the spacing existing between the wall of the die and the surface of the male punch adjacent the recesses ll and 12. This increased thickness is provided by diverging surfaces formed between the zone 15 and the cavity 8. Thus, at diametrically opposite places of the cavity 8, and intermediate the places where the bosses 5 and 7 are formed, the cavity 2 is outwardly tapered, as indicated by the areas 2.8. These surfaces 13 extend entirely to the open upper end of the die 1 from a lower boundary or level 35, this boundary being in a plane transverse to the axis of the punch which passes through the wrist pin recesses ll. and 12. The surfaces 18 are conical and diverge upwardly. They cooperate with the zone 15 of the punch 2 to define a pair of outwardly diverging space sections conforming to the portions l6 and 17 of Pig. 5. These outwardly diverging annular spaces serve to reduce the inequality in the rate of flow of the metal when the punch 2 is brought into fully cooperative relation with the die 1, as illustrated in 4 and 6, by promoting the flow of metal into the skirt portions while simultaneously metal is flowing into the recesses El and 12 to form the bosses.

As the punch 2 moves into the die cavity 8, the metal the male punch in areas adjacent the recesses to the opposing wall of the die cavity; such restriction prevents the metal from flowing to an excessive height above the wrist pin bosses and insures a complete filling of the recesses 11 and 12 with metal of proper grain structure and without voids. These recesses receive a large amount of metal and in order to prevent the skirt areas (in portions at to the recesses) from being starved, from failing to receive an adequate supply of metal and from being retarded in their completion, resistance to metal flow is reduced in the areas 16 and 17 and it will be noted that such reduction in resistance is accomplished by increase in the spacing between the surface of the punch and the die wall. erably starts at a level or plane passing through the recesses i1 and 12 so that metal is caused to flow upwardly to form the skirt portions (between wrist pin bosses) at the same time that metal flows into the recesses to form the wrist pin bosses, thereby producing uniform upward rise of metal throughout all areas of the annular space between the punch and the die. Control zones of resistance and relief are thus established which permit the production of piston blanks with an open skirt end terminating in a plane substantially trans verse to the axis of the blank as shown in Figs. 4, 6

and 7, i. e. the skirt is of virtually uniform length around its entire periphery and the skirt length does not vary with the proximity of a wrist pin boss. As a result the metal on the skirt is uniform in texture, grain and physical properties and all of the metal of a slug is effectively utilized.

The angle between the surfaces 15 and 13 may be of the order of 1 to 4, the specific angle being dependent upon the particular configuration of the interior surface of the hollow article to be forged. The easier the flow of metal. into the wrist-pin boss cavities 11 and 12, the larger this angle should be to reduce the inequality of the resistance to flow. In the resultant blank, at diametrically oppositc places intermediate the wrist pin bosses 6 and 7,--there is a thickened portion of the wall, but this elliptical-like configuration is tmed in the process of machining.

The angles on the punch .2, at the points of change in dimensions needed to form irregular shapes, are

critical, and depend on the amount and speed of the material to flow over them. Radii should never be used except in the caseof a reverse radius, such as the fillet 22. Angles of 90 are ideal. When the end use of the product prohibits the use of 90 angles, other angles producing fiat surfaces between them are permissible. However, the angles used depend on the amount and speed of the material to be moved over them. When forming thin walls, necessitating fast flowing material, the volume being dependent on the length of the wall to be formed, the angle at the edge of the punch must approach a right angle as nearly as practical to form the desired object. When a thick wall is to be formed, utilizing slower moving metal, the angle may be less than 90 to a greater extent. However, the angle must never be such that it causes a wedging effect between the punch and walls of the die cavity or elsewhere. This principle is illustrated, as at the zone 19 (Figs. 2 and 3) forming the leading edge.

Thus, this zone 19 is defined by a cone having straight line elements. These elements make approximately an angle of 45 with the adjacent zones of the punch. Accordingly, any plane passing through the center line of the punch 2 will intersect zone 19 along a straight line.

When the single impact-extrusion step is formed by bringing the punch 2 into full cooperative relation with the die 1, the blank 3 may be removed after the punch 2 is withdrawn by the aid of the stripper portion 38 that may be extended upwardly into the cavity 8.

When blanks are thus produced by the impact-extrusion process, the punch 1 generates heat. When running the press at production rate, the punch usually soon becomes too hot for continued use. However, when the press is started, it is necessary to heat the punch 2 in order to reduce the shock loading that would otherwise occur.

Such enlargement pref- A temperature control system for this purpose is diagrammatically illustrated in Fig. 1.

The punch 2 is provided with a plurality of cavities 24. Into these cavities extend pipes or conduits 25, forming, with the cavities, narrow annular passages ex tending longitudinally of the punch 2. A common inlet conduit 26 serves to pass liquid downwardly through the conduit 25. The liquid is discharged into a common outlet conduit 27.

Another cavity 323 is provided substantially centrally of the punch 2; and within this cavity is placed an electric heating element 31, such as a calrod. Connections 32 are provided for this element.

A thermostatically controlled system 33 is provided which serves either to energize the heating element 31 or to place a cooling system 34 into heat exchanging relation with the liquid passing into conduit 2a. In this way, the temperature of the punch 2 can be maintained at the desired level.

I claim:

1. In an impact extrusion apparatus for forming forged metal piston blanks, said blanks having an integral head, a hollow skirt portion and wrist pin bosses extending in wardly of the skirt portion and spaced from the end of the skirt: a die provided with a cavity having walls adapted to form the outer surfaces of a piston blank; a punch cooperating with the die, said punch being provided with oppositely disposed recesses adapted to form Wrist pin bosses; the wall of the die and the surfaces of the punch being relatively close together in the region of the recesses to thereby restrict flow of metal from each recess into skirt portions adjacent thereto; the surfaces of the punch and walls of the die being further apart in zones between said recesses from a transverse plane intersecting said recesses to the end of the skirt to promote and facilitate the flow of metal into said zones, whereby a skirt is formed of nonuniform thickness in various planes above said recesses.

2. Apparatus of the character stated in claim 1 wherein the surface of the punch in the zones between recesses is spaced progressively greater distances from the Walls of the die with increasing distance from the head of the blank.

3. in an apparatus for forming forged metal piston blanks having integral wrist pin bosses by impact extrusion, the combination of: a die and a male punch having surfaces cooperating with the die, said male punch including a pair of oppositely disposed recesses adapted to form wrist pin bosses, the surfaces of said die and punch defining a space for the reception of metal for the blank; the surfaces of the die and punch adjacent each wrist pin recess being relatively close together to thereby restrict the flow of metal from each recess into skirt portions adjacent thereto; the surfaces of said punch and die being further apart in zones between said wrist pin recesses from a level intersecting said recesses to the end or" the skirt to promote and facilitate the flow of metal into said zones.

4. in an apparatus for forming a forged metal piston blank having a head, a skirt of non-uniform thickness but virtually uniform length and integral wrist pin bosses, by a single stroke impact extrusion, the combination of: a die having walls and a male punch having surfaces cooperating in spaced relation with the walls of the die to form a space therebetween for the reception of metal, said male punch including a pair of oppositely disposed recesses adapted to form wrist pin bosses; means for controllably heating and cooling said punch; the walls of the die being spaced from the surfaces of the punch and cooperating therewith to form a space therebetween for a skirt including opposing skirt portions of increasing thickness between said wrist pin recesses and extending from a transverse Zone passing through said recesses to the end of the skirt; the wall of the die' and surface of the punch adjacent and above the recesses of the punch being relatively close together to restrict flow of metal upwardly from said recesses, the wall of the die and the surface of the punch being further apart in portions between recesses to promote and facilitate upward flow in said portions, whereby a skirt of nonuniform thickness but of virtually uniform length is obtained.

5. The method of making a forged piston blank provided with a head, a skirt of virtually uniform length and integral wrist pin bosses, by a single impact extrusion operation of a male punch against a slug of metal in a die, consisting of forming a thin skirt adjacent each wrist pin boss by restricting and impeding the flow of metal into skirt portions adjacent each of the wrist pin bosses being formed, and simultaneously forming a thick skirt in portions between wrist pin bosses by promoting flow of metal into skirt portions between said'bosses, whereby the resulting skirt is of virtually uniform length but of greater thickness between bosses than immediately above said bosses and is free from defects.

6. An apparatus as stated in claim 3, wherein the punch is substantially cylindrical in cross section above a transverse plane passing through said recesses and the surfaces of the die are non-circular in cross section in and above said plane.

7. in a method of making a forged metal piston having an integral head, a skirt and wrist pin bosses, the steps of: forming a piston blank by a single impact extrusion operation by a male punch against a slug of metal in a die, restricting the flow of metal into skirt portions adjacent each of the wrist pin bosses being shaped to form a thin skirt adjacent and above each wrist pin boss, and simultaneously forming a thick skirt in portions between wrist pin bosses by promoting flow of metal into said skirt portions between Wrist pin bosses to form a piston blank having a skirt of virtually uniform length but of greater thickness between bosses than immediately adjacent to and above said bosses, said blank having a noncircular, elliptical-like external contour along transverse planes through said bosses and thereabove; and then machining said blank to convert said external contour to cylindrical form.

References (Iited in the file of this patent UNITED STATES PATENTS 

